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No, that is not correct. A hermaphrodite species will all things being the same have twice as many offspring as an asexual species, in your example 1000 from it

No, that is not correct. A hermaphrodite species will all things being the same have twice as many offspring as an asexual species, in your example 1000 from its eggs, 1000 from its sperm. In a strictly male/female species, a successful female will indeed likely spread the genes half as fast, but a succesful male can spread them much faster. But this is with only one gene. Imagine there are five a, b, c, d and e. An individual with all five will arise much sooner in a sexual species. The evolution of sex isn't a mystery any more than an eye is a mystery. It's not all or nothing. Life didn't go from bacteria to peacocks in one step. You can have something like optional hermaphrodite sex (in mollusks, I think) where you can exchange genes when the conditions arise, but it's not mandatory. The costs are virtually zero, but the benefits are still there. But then it becomes advantageous for idividuals to cheat and impregnate others, without producing eggs themselves and you get separate sexes.

jballanc 11y ago
Absolute numbers don't matter, only frequency, as in evolution you have to assume that individuals are reproducing fast enough to exceed the carrying capacity of the environment. And yes, once you get to more mutations then sex is more advantageous for a number of reasons. No one is claiming that sex is not better over long enough time scales. The question is how can it be advantageous enough to become fixed in a population over the span of a couple generations. And yes, sex did evolve gradually. Slime molds have optional sex (and more than 2 sexes!). But still keeping the machinery around is expensive. One would expect that individuals that ditched it would outcompete those that kept lugging it around unless there was a relatively short-term benefit to sex.
- PepeGomez 11y ago
  Exactly, in a stable population, one offspring of each individual survives on average in an asexual species. Two with half of your genes each survive in a sexual species. It doesn't need a long timescale, asexual species get out-evolved by sexual species and go extinct eventually. Sexual species have a much higher probability of entering new niches or surviving when the conditions change. This can be seen in many species that reproduce asexually when the conditions are good, but reproduce sexually when stressed. A species that loses the ability to reproduce sexually is doomed to extinction. Asexual reproduction is essentially putting all your eggs into one basket. When you die of a disease for example, chances are that most of your offspring dies as well AND there is a much higher chance that the disease adapts to your genome in the first place. This can be seen in agriculture, where plants are reproduced asexually to a much bigger extent than what would happen naturally. Many are impossible to grow without heavy doses of pesticides, as the diseases quickly adapted to the commonly planted strains. The strains need to be replaced every few decades, before growing them becomes essentially impossible, even with pesticides. Evolution is much faster than you assume.

jballanc 11y ago

Absolute numbers don't matter, only frequency, as in evolution you have to assume that individuals are reproducing fast enough to exceed the carrying capacity of the environment. And yes, once you get to more mutations then sex is more advantageous for a number of reasons. No one is claiming that sex is not better over long enough time scales. The question is how can it be advantageous enough to become fixed in a population over the span of a couple generations. And yes, sex did evolve gradually. Slime molds have optional sex (and more than 2 sexes!). But still keeping the machinery around is expensive. One would expect that individuals that ditched it would outcompete those that kept lugging it around unless there was a relatively short-term benefit to sex.

PepeGomez 11y ago
Exactly, in a stable population, one offspring of each individual survives on average in an asexual species. Two with half of your genes each survive in a sexual species. It doesn't need a long timescale, asexual species get out-evolved by sexual species and go extinct eventually. Sexual species have a much higher probability of entering new niches or surviving when the conditions change. This can be seen in many species that reproduce asexually when the conditions are good, but reproduce sexually when stressed. A species that loses the ability to reproduce sexually is doomed to extinction. Asexual reproduction is essentially putting all your eggs into one basket. When you die of a disease for example, chances are that most of your offspring dies as well AND there is a much higher chance that the disease adapts to your genome in the first place. This can be seen in agriculture, where plants are reproduced asexually to a much bigger extent than what would happen naturally. Many are impossible to grow without heavy doses of pesticides, as the diseases quickly adapted to the commonly planted strains. The strains need to be replaced every few decades, before growing them becomes essentially impossible, even with pesticides. Evolution is much faster than you assume.